The present invention relates generally to inspection systems, and more particularly to an optical inspection system for checking the presence of poor conditions of mounted parts on a substrate such as position inaccuracy, lacks, rising and soldering fault of parts packaged or installed on a printed-circuit board.
Recently, improvement is being made for size-reduction and high-density packaging of parts to be installed on a printed-circuit board, whereby difficulty is encountered to accurately check the packaging conditions of the parts on the printed board through the visual inspection. In order to cope with such a situation, there has been proposed a system which automatically inspect the packaging conditions of the parts on the printed-circuit board on the basis of data optically taken through an optical apparatus such as a video camera and others. There is a problem which arises with such conventional optical inspection systems, however, in that difficulty is encountered in obtaining accurate data in terms of the heights of the parts on the printed board due to regular reflection light from metallic surfaces of the parts and printed-circuit board, shadows of the parts, and others. In addition, in cases where the intensity of the reflection light from the printed board and/or the parts thereon due to illumination of a light beam is extremely high or low, it is difficult in practice to accurately and quickly measure the height data for all the parts on the printed-circuit board, because of difference in dynamic range between the reflection light and an image-processing unit for processing an image due to the reflection light so as to obtain height data of the parts on the printed-circuit board. This causes inspection for only given parts to be unavoidable so as to reduce the inspection accuracy as a whole. Thus, a further improvement is required with a view to heightening the accuracy of the height data of the parts to increase the inspection accuracy.